Here you go. Thinking about it a bit more as I was drawing it I think you don't need any extra resistors to get clean switching as the amps input will never have its input broken away from being able to source current.

Use a DPDT switch, the top half shown above is the normally closed ones and the bottom/right is the normally open ones.

The only downside to this is you would either need two switches or a quad gang one to switch stereo passively. If you used relays to switch the signal then you could still use the one switch but you would obviously then need a battery or power to run the unit.

Looks simple enough, I suppose the only thing to do is try it and see if it is quiet. The only downside is that I need the switch to be a foot operated device and DPDT seems quite rare in foot operated components, SPDT is the more common. My ideal would be a momentary action switch with the electronics providing the latch, but this would mean more complexity

Thanks for your replies. I would like if possible to reduce it to point where it couldn't be heard rather than just reduce the volume. Andy's idea of a small DPDT relay could be a good idea as I could aslo add an LED to indicate the swtiches state easily. I am just uncertain if the resistor switching can be relied on not to click or pop during switch in and out. I will need to try a few experiments to see.

Geek, do you have any circuits for using a Bi-Polar transistor for the mute as I *never* seem to have much luck with FET circuits with signals as high as 2.5v pk and using 9v batteries

The one used by Yamaha for a decade was just a 4.7-10K resistor in series with the output, collector to that on the output side, emitter to ground, base to the controller chip through a little R-C circuit for shaping. There was no Vcc on the collector.

Tried it on a breadboard with a 2N5088 and worked well for line level mute

I tried this circuit attached based on a transistor I have knocking about and it seems to work quite well and I get at least -50dB reduction in volume. Is this what you mean?

The 2.2K series resistor is about as high as I want to go as I want to feed a 20K amplifier line input. Not sure if I have suitable values for the R-C components in the transistor base, or indeed if I have the R-C bit configured correctly. Can you experts give me any pointers here?